With the increasing improvement of A/D converter quantization accuracy, the requirements to the linearity thereof are higher and higher. Sampling linearity is a critical factor for A/D converter linearity, and a large amount of applications require lower A/D converter power consumption, and thus, a sampling device with high linearity and low power consumption is required. However, the traditional sampling device usually generates second-order non-linearity during capacitance sampling (that is, the sampled capacitance value includes second-order terms relevant to the input voltage), thus causing low linearity of the sampling device.